Premium Fuel

Every time I go to the petrol pump (that's gas station for you Neeraj), the attendant asks me if I wish to buy POWER, and never tires of reminding me that the difference is now less than Rs 2.5. When I asked him why I should pay a few bucks more, his answer was typical of everyone on the sell side of commodity products in India. "Quality achcha hain." When I asked how, he stared at me and said, "It is better."

Right. Better for who? I am sure it is better for him; clearly there is some sort of incentive structure in place for him to take the trouble of trying to sell me every single time. But is it really better for me? A couple of times, I succumbed to the sales pitch and chose the premium fuel, and tracked my fuel economy under similar driving conditions. The difference in fuel economy, I will have you know, is zilch. Nada. Zero. I have tried this on my city commute and on my expressway runs to Mumbai. Have tried it under controlled speeds i.e. 100 kmph on the expressway and at my regular speeds - which I shall not mention here for fear of losing my driving licence.

So is the premium fuel really any better? For the buyer that is? As it turns out, after a little it of research on the internet, not only is it not-better, but it might even be adversely affecting your engine. The number on the fuel, 87 or 91 is an index of the compression the air fuel mixture can withstand before it ignites. Car manufacturers design engines with a certain compression ratio and they recommend a fuel for their engines. If you buy premium fuel, rated say 91 for your car for which the recommended fuel is regular, say 87, then not all of the the air fuel mixture is going to ignite when the engine expects it to, and you are likely to be getting lower efficiency and fuel economy. Conversely, if you have a high performance car with a high compression ratio engine that is designed for use with a higher rated fuel and you use the regular stuff, then some of the fuel is getting ignited too early and you might need to adjust the timing on your engine. The only cars that could possibly benefit from either fuel are the ones that are designed to detect the quality of the fuel and change the ECU remap accordingly to make best use of the available fuel.

So the next time, the petrol pump attendant tries to sell you the premium stuff, you can tell him exactly where to put that nozzle. Back in its receptacle of course.

Source: http://en.wikipedia.org/wiki/Octane_rating http://www.reddit.com/r/explainlikeimfive/comments/31p35y/eli5_other_than_efficiency_what_does_pumping/